1. Field of the Invention
The present invention relates to the preparation of diorganopolysiloxanes having alkoxy end groups (hereinafter designated FP: functionalized polymers), and to their use as one of the essential constituents of single-component organopolysiloxane compositions which are stable in storage in the absence of moisture and which are crosslinked into elastomeric state by atmospheric moisture at ambient temperature, hereinafter designated cold-vulcanizable elastomeric compositions (CVE).
2. Description of the Prior Art
Many processes for preparing diorganopolysiloxanes having alkoxy end groups are known to this art.
The processes described in U.S. Pat. Nos. 3,122,522, 3,161,614 and U.S. Pat. No. Re. 2,970 are especially representative. The processes described in these patents are not presently being carried out industrially because they are either too costly or result in the production of FPs of too poor a quality for their intended use as a base polymer for CVE compositions.
A notable advance in the art is reflected in U.S. Pat. No. 3,542,901, describing a process for the preparation of FP by reacting an alpha,omega-dihydroxydiorganopolysiloxane polymer, otherwise known as a diorganopolysiloxane having silanol end groups, with a polyalkoxysilane in the presence of a functionalization catalyst containing an amine functional group.
This process is undoubtedly effective, but it is very difficult to properly remove the amine, which may have a detrimental effect on the storage stability of the CVE composition in the presence of the condensation catalyst, which is a compound of a metal, generally tin.
Other catalysts may be employed, such as, for example, an organic titanium derivative (U.S. Pat. No. 4,111,890), an alkoxy aluminum chelate (British Patent GB-A-2,144,758) and an N,N-disubstituted hydroxylamine (French Patent Fr-A-2,508,467). These catalysts can present the disadvantage of being relatively inefficient or adversely effecting on the storage stability of the CVE compositions.
Another process for making FPs entails employing mixed silanes which contain, in addition to alkoxy groups, a hydrolyzable group such as an amido, amino, carbamate, oxime or similar group, optionally in the presence of a known functionalization catalyst and of a polyalkoxysilane.
Processes of this type are particularly described in U.S. Pat. Nos. 3,697,568 and 3,896,079, and in EP-A-69,256.
These processes are efficient, but require the use of costly mixed silanes Furthermore, the organic products resulting from the groups which can be hydrolyzed after reaction can have a detrimental effect on the CVE composition (in this regard, see pages 4 and 5 of French Patent FR-A-2,543,562).